High-frequency discharge pumped axial-flow lasers are now used for a variety of applications, due to advantages such as a high-power output, high-quality beam, stable oscillation, high-speed control capability and the like.
A conventional axial-flow type high-frequency discharge pumped laser device is illustrated in FIG. 6. In FIG. 6, numeral 1 denotes a discharge tube, which comprises four tube segments in the illustration but may have any desired number of tube segments depending on the output to be produced, and these tube segments may be arranged in parallel or in series with each other; 2 and 3 denote a total reflection mirror and an output mirror, respectively, which are accurately positioned; and 4 denotes an outgoing laser beam. The segments of the discharge tube are provided with inlet and outlet ports connected to a single Roots blower 7, and heat exchangers 5 and 6 are used to cool a laser gas heated by the electric discharge and the compressing action of the Roots blower 7. The laser gas flows in the discharge tube 1 and gas delivery tubes in the directions indicated by the arrows. The gas flows in the discharge tube 1 at the speed of about 100 m/second. Electrodes 8a, 8b to 11a, 11b are connected to respective high-frequency power supplies 12, 13, 14, and 15, and an electric discharge is produced by a high-frequency voltage from the high-frequency power supplies 12 to 15, to generate laser oscillation.
In this type of high-frequency discharge pumped laser device having plural discharge tube segments driven by respective independent high-frequency power supplies, the laser output fluctuates in the cycle of several hertz. This laser output fluctuation is illustrated in FIG. 7, wherein time is indicated along the horizontal axis and the laser output is indicated along the vertical axis. As seen from FIG. 7, a laser output of about 1,000W is subject to an approximately 30W fluctuation.